[mjklaser]

**MPG UPDATE: 42.8 corrected, see my latest post for details**

Today, I did an airbox mod that was inexpensive, made a pretty big improvement in acceleration through all gears, and is 'tunable':



I got the idea years ago from a post by "Ammo Man" on 08/18/2009 (Thanks, Ammo!). This weekend, I had 3 stuck screws that I had to drill out to get the airbox cover off. So, I figured I'd do this as an experiment to get more air flow into the carb in a tunable way (more on that later), since the cover is kind of ruined anyway. I'll take you through how I did it. First, I laid out the position of the 'ports' (windshield washer jet covers per Ammo Man) on the airbox cover using blue painter's tape, and I drilled pilot intake holes on-center:



Here's a pic of the backside of the cover:



Then, I carefully scribed the tape with a sharp razor and removed it to form a 'position template':



The airbox cover is curved and the 'windshield washer jet covers' (ports) are flat:



So, I used the cover as the 'curvature template' and ground the proper curvature into the ports:



The difference is subtle, but very real and much needed:



When the curvature is matched, they fit nicely:



To attach the ports, I used Scotch-Weld 2216 epoxy that I had on hand:



Here are the radius-matched ports, masked cover, and epoxy ready to go:



A little dab of epoxy on each end:



I positioned the ports on the cover using the 'template' and taped them down to prevent sliding out of position. Put in the oven (with door open and at 200F on bake) to speed-cure the epoxy (~1 hour):



After full cure, pulled off the tape:





Installed the cover on the bike after cleaning/oiling the K&N filter:





If you look closely you can see the mucked up screws that were stuck and I had to drill out... (and are now missing because the black airbox inserts are gone). I have a new airbox and cover coming from Ron Ayers to get that all fixed up... Now, about being tunable: I drilled small pilot holes (~ 5mm or 0.200") and can open them up in small steps until I get the proper air flow that gives me the best air:fuel ratio for optimum power in all rev bands. If I go too big on the holes, I can epoxy washers on the backside of the cover to restrict, or just block one or two of the holes, giving me the tunability I was looking for and can't achieve with the other common airbox mods here on the Cafe (also, see Post #20, in this thread).

I took the bike out for a 70-mile ride tonight after the mod was complete, and I noticed the improvement already (with just the 5mm pilot holes). I will see what I can do without re-jetting, just optimizing the hole diameters, then go from there... but I am already very pleased with the results...

'laser atriot:

 

[Falcon518]

Thats a good write up. sometime in the not too distant future I will be de-capping, and re-jetting, I like what you did to the cover, looks really good.-cheers

 

[mjklaser]

I've had a couple PM's already asking about the ports. They are Pilot p/n IP-2001, come in packs of two, and are $4.99 per pack. I bought two packs at Autozone, all they had, so I went over to Advance Auto and they had them too.

http://www.autozone.com/autozone/ac...zzle-covers/_/N-259c?itemIdentifier=65805_0_0_

I used the Scotch-Weld 2216 Epoxy because I had it already, but it is damn expensive... I'm sure that J-B Weld epoxy works just as well and you can find that at pretty much any auto parts or hardware store, or at Amazon, for about $6:

http://www.amazon.com/Weld-8265S-Compound-Epoxy-Twin/dp/B0006O1ICE/ref=pd_sim_sbs_indust_2

BTW, the area of the 5 small holes is equivalent to a single 1/2" diameter hole - I know that doesn't seem like much but the ports 'capture' air and force a right angle turn into the airbox - kind of a poor man's 'ram air' induction. I plan to gradually increase the holes' diameters - I could go up to as much as 1/2" diameter each due to the width of the ports, but I'm certain that would require a re-jet, which I wanted to wait on, for the time being (also, see Post #20, in this thread).

 

[mdolph]

Airbox Mod! "Penta Micro-Charger": $15, tunable, and big performance gain

Looks slick, nice job! Great write up as well!

 

[Gonzo1970]

Now, if I still had a Stock Air Intake, I would seriously consider this.. Pretty slick!!

-Gonz

 

[Jag75]

Re: Airbox Mod! "Penta Micro-Charger": $15, tunable, and nice performance gain

I like the looks of that

Sent from my HTC PH39100 using Tapatalk 2

 

[BigBoreVTX]

Cool looking. Really nice wright up.

 

[eXo]

I'm gonna have to give this a go. The stock air box is too plain.

 

[SPyKER]

Very cool look! I've looked for a way to incorporate a scoop but the ones they make that would work with a 80mm hole are HUGE and look very wrong! Your look is very clean and direct.

Honestly, I would look at opening them as much as you can and seeing what you can do with just shimming the needle (scar mod). The stock jets can provide a lot more than many think, and I ran that way with two shims for three years with the 80mm hole I open up.

I was working on something similar for my mod once I get my 3D printer and vacuum molding setup in place, but that could be months away.

 

[Bassdude404]

Pretty cool looking mod!!...If I didn't already have a custom cut cover, I'd be all over this!!....

 

[Greg Riddle]

looks nice

 

[robdan51]

Great looking mod.Think I will have to give it a try.I hope it turns out as good as yours.Thanks for the great write up and pics.

 

[phil9182]

Looks Great! Is there a need to do any rejetting? I am all stock except for cobra slip ons. Thanks!

 

[mjklaser]

Thank you, everybody, for your positive comments! :cheers:

To answer phil9182's question: There is no re-jetting necessary if the total surface area of the holes is kept below a 'certain amount'. I don't know what that value is yet. I plan to open up the hole diameters in small increments, test (feel the ride), repeat - until the improvements gained start to diminish - meaning that, at some point, the A/F mix will get too lean (this is why I took this approach - it is 'step-wise' tunable). Then I can go back to the 'optimum' hole diameters by epoxying washers with the required hole size to the back side of the cover - or just block off one of the holes to replicate the total hole surface area of the best-performance case (also, see Post #20, in this thread). Or, I could just do a new one - the airbox covers are only $24.50 at Ron Ayers Motorsports (ronayers.com). Years ago, I installed aftermarket pipes (Cobra Speedster Slashdowns), did the Scar Mod (1 shim, 2-1/16 turns out), and performed the PAIR valve removal - just so that you all are aware of my exact set-up...

To those planning to do this mod, a couple of finer points regarding my write-up: Since the airbox cover is curved (convex) where the ports (aka 'scoops' - thanks SPyKER - why couldn't I think of the word 'scoops' when I did the write-up?) are located, they tend to slide off when you are trying to arrange them on the blue painters' tape - very frustrating. So, I taped them down by their ends with scotch tape (with the loose ends of the taped folded over so I could easily pick them up again). Then I played around with the position of all of them 'til I got the best alignment, spacing from each other, centration on the cover, etc. When I was finally happy with the location of all five scoops, I traced their outlines with a pen as seen in the 2nd photo. That's why you don't see the 'ends' of the scoops traced in that pic - that's where the scotch tape was. Secondly, when I speed-cured the epoxy in the oven, I slid the middle rack out as far as it would go - the oven felt too warm on its lowest setting (200F), so by sliding out the rack, the airbox cover was actually outside (in front of) the oven. I didn't want to melt/deform the plastic! I put a cookie sheet on the rack, then aluminum foil on the cookie sheet. There is no direct need to heat-cure, you could just let the epoxy cure at room temp for 24 hours - but I was doing this on a Sunday and wanted to try it out that afternoon!

This is an experiment in progress, so please stay tuned for updates. In fact here is update #1:

I've put 140 miles on since I did the mod - and I must say, it's been the most fun I've ever had with the bike. The acceleration is better in all gears, especially in 3rd, 4th & 5th - these speeds are where the 'ram-air induction' is really doing its thing. There are no flat spots in acceleration, and no backfiring or any improper sounds. I'm (finally) tapping into the real potential of this engine - glad I did this mod... and all this is just with the five 0.200" pilot holes. Hahahaaaaa... more to follow...

'laser atriot:

 

[beriah]

Like the looks of that, good to see new things!

 

[Falcon518]

Can you do this mod and decap?, or would that be too much? Only reason why I ask is and my understanding, if you decap then you don't need to keep taking the tank off.

 

[Vinish]

Now you need to figure out how to add some sort of sliding block-off plate on the inside of the cover. This would allow you to drill large holes and then adjust the air flow on the fly by sliding this hypothetical plate.

G'day,

Vinish

 

[Endy]

Now you need to figure out how to add some sort of sliding block-off plate on the inside of the cover. This would allow you to drill large holes and then adjust the air flow on the fly by sliding this hypothetical plate.

G'day,

Vinish

That's exactly what I was thinking Vinish. Still a very cool mod, though.

 

[FlyingScotsman]

Awesome! I saw this exact mod at a rally on Eglin AFB last month, loved the look and have been looking EVERYWHERE for a "Pilot Air Cover" haha! Who'd have known. I wanted some more airflow but love the stock box look, so this is perfect. Thanks for the write up man! I'll be back to see what ya find out about the hole diameter.

 

[mjklaser]

Can you do this mod and decap?, or would that be too much? Only reason why I ask is and my understanding, if you decap then you don't need to keep taking the tank off.

Falcon, I would think that if you do the airbox de-cap, then you don't need this, and vice versa - but if you do both, you would have to re-jet the carb for sure...

Vinish and Endy, good idea!

Scottsman, besides the look, it's totally unobtrusive as well - my upper calf only touches the cover behind the scoops (if I 'squeeze' the tank), so I could never feel them even if I try... that was another factor for my going this way...

I did a quick calculation and determined that at 60mph, because of their frontal open area of 0.63" height x 0.31" width each, the 5 scoops capture 1035 cubic inches of air per second (or 16.9 Liters/sec). That seems like quite a bit, but I checked my numbers three times... I don't know what percentage that is of the total airflow that the airbox takes in at 60mph, but I would like to figure that out at some point, to have a reference value.

'laser atriot:

P.S. Hmmmm... Since doing that calculation and now that I am really thinking about the physics of this, I don't think that the hole diameters make much of a difference above a certain size. Air is compressible, so pretty much, whatever the scoops capture will make it into the airbox. A larger hole diameter will only decrease the velocity at which the 'swallowed' air enters the airbox - smaller hole, higher velocity. I think the only way that I could significantly increase the amount of air captured (with this method) would be to add more scoops (and there is not much more room), or use larger ('taller') scoops. I could decrease the volume of air captured by blocking holes at this point... but I don't want to do that because it's currently running GREAT! Food for thought... anyway, I already have a new cover from Ron Ayers, so I could try to fit six scoops by making them touch. In the meantime, I will still open up the hole diameters and let you all know if that makes any perceivable improvement...

UPDATED June 6th, 2013: Okay, sorry for waffling about on this, but after hitting my textbooks researching this further, I find that I was right the first time - this approach IS definitely 'flow-rate' tunable by the diameter of the holes going through the airbox cover (and not just dependent on the scoop opening's cross-sectional area). I think I must have partied too hard during the semester I took fluid dynamics...

However, the air flow rate into the airbox is not hugely dependent on the hole diameter until the holes get very close to the same cross-sectional area as that of the scoops openings. For example, if I increase the cross-sectional area of the holes from "20% of the area of the scoops" to "80% of the area of the scoops", then the total flow rate of air into the airbox only increases by a factor of 30% (1.3x). But, if I increase the area of the holes from "20% of the area of the scoops" to "95% of the area of the scoops", then the flow rate into the airbox increases by 130% (2.3x)!

In other words, making small incremental changes in the hole diameters as I had planned will only make very small changes in air flow into the box. If I want to really experience a difference in performance (for better or worse) from where the holes are at now, then I will have to get pretty aggressive about opening them up. This is what SPyKER suggested earlier, but without the math. But, my bike is running so great right now, I kind of wonder how there can be any more to get...

'laser atriot: